1. Field of the Invention
The present invention relates to a light emitting device and a method for manufacturing a light emitting device.
2. Description of Related Art
A light emitting device using a semiconductor light emitting element (hereinafter simply referred to as “light emitting element”) such as a light emitting diode (LED) may be used as a light source for display devices and illuminating devices. Light emitting devices using light emitting elements are attracting attention as new light sources to replace conventionally used fluorescent lights, filament lamps, and the like. Particularly, an LED has a long life in comparison with other light sources, e.g., a fluorescent light or a filament lamp, and is capable of emitting light with less energy. Therefore, the LED is largely expected to be the next-generation light source for lighting.
Demand for light emitting devices of white light is most expected. Known light emitting devices include those including light emitting elements of red light, blue light, and green light to emit white light, and those emitting white light by using a light emitting element and fluorescent materials capable of emitting complementary colored light when excited by the light emitting element. For a light emitting device used for general lighting, if the light emitting device uses the light emitting elements of colors of red, blue, and green, a color rendering property thereof is degraded. Thus, a white light emitting device using fluorescent material is preferred. More specifically, a white light emitting device using a blue light emitting element and YAG fluorescent materials is known.
A light emitting device configured by using the light emitting element and the fluorescent materials is prepared by forming a phosphor layer such that the phosphor layer covers the light emitting element. However, recently, a light emitting device provided with the light emitting element mounted in a case by using a submount has been used. In such a light emitting device, various improvements may be made in order to improve flux while preventing luminance from being degraded.
For example, a light emitting device having a configuration in which a reflective layer mixed with titanium oxide is provided around a submount mounted with a light emitting element within a resin case, and formed with a light-transmissive layer containing fluorescent material so as to cover the reflective layer and the light emitting element has been disclosed. See, e.g., Japanese Patent Publication No. 2005-026401 A.
Further, a light emitting device having a configuration in which a primary sealing member is filled around a submount mounted with a light emitting element so as to cover upper side surfaces of the light emitting element to cure the primary sealing member within a resin case and, subsequently, a secondary sealing member containing a fluorescent material is filled on the primary sealing member to forcibly precipitate the fluorescent material on an upper surface of the light emitting element and an upper surface of the primary sealing member to cure the secondary sealing member has been disclosed. See, e.g., Japanese Patent Publication No. 2008-218511 A.
The light emitting devices disclosed in, for example, Japanese Patent Publication No. 2005-026401 A and Japanese Patent Publication No. 2008-218511 A, had a problem that there occurs color unevenness and a yellow ring as the phosphor layer becomes larger with respect to a light emitting portion of the light emitting element.
To solve the above problem, forming a phosphor layer only around the light emitting element according to electrode positioning and printing have been studied. However, the electrode positioning has the following problems. Namely, a particle diameter of the fluorescent material is limited and thus classification of the fluorescent material is essential. Further, the phosphor layer is formed also on terminals and wire parts charged with an electric potential. Still further, a light emitting element specially treated so as to cause the entire light emitting element to have an electric potential becomes essential.
On the other hand, printing has the following problems. Namely, it is difficult to form the phosphor layer since the light emitting element including an electrode on an upper surface thereof requires a wire interconnection. Therefore, use of the printing is limited to a case where the light emitting element of a flip-chip assembly type is used, and a problem in printing precision is seen in the printing.